One aspect of the present invention involves sending out a pulse and waiting for another pulse to return. The time delay between the two pulses is an indication of the distance from the transmitting source to the receiving source. The uniqueness of this aspect is that acoustic pulses are sent out and acoustic pulses are received. An acoustic transmitter-receiver and an acoustic receiver-transmitter assembly are used. The acoustic receiver-transmitter assembly is under the direction of the acoustic transmitter-receiver. Immediate response by the acoustic receiver-transmitter assembly in the direction of the acoustic transmitter-receiver is important and allows one to obtain an accurate measure of distance. This distance information is obtained by measuring the turn around time between transmission of a pulse and receipt of a pulse by the transmitter-receiver.
A second aspect involves is the use of the receiver-transmitter assembly at the bottom of the ocean that sends out a continuous signal. The receiver-transmitter assembly is turned on as a result of a signal from the transmitter-receiver. A signal of a continuing duration and of a precise fixed frequency is sent out in all directions by the receiver-transmitter assembly. The transmitter-receiver may be on board a vehicle such as a submarine. The transmitter-receiver detects the fixed frequency signal. The transmitter-receiver measures the apparent frequency of the fixed frequency signal. The vehicle also knows the true frequency of the fixed frequency signal that is being sent out by the receiver-transmitter. An amount of difference in frequency, between the apparent frequency detected by the vehicle and the true fixed frequency, is an indication of an amount of velocity of the vehicle with respect to the receiver-transmitter assembly. The amount of shift in frequency is an indication of the velocity of the vehicle.
A third aspect of the invention is the use of a receiver-transmitter assembly at the bottom of the ocean to carry out the two above described functions. One function is immediate response by means of a pulse in response to receipt of a transmit pulse. Another function is response by means of a continuous fixed frequency signal in response to a receipt of a command signal.
A fourth aspect of the invention is a system that uses several bottom receiver-transmitter assemblies and thereby provides both position and velocity information to a vehicle. The position information is the result of the fact that the locations of several bottom receiver-transmitter assemblies are known with respect to the earth and that the distances from the vehicle to these bottom receiver-transmitter assemblies can be calculated. The velocity determination is due to the fact that the locations of several bottom receiver-transmitter assemblies are known with respect of the earth, and the position of the vehicle and velocities of the vehicle, with respect to these bottom receiver-transmitter assemblies, can be calculated.
Patent application Ser. No. 281,139, filed Dec. 7, 1988 shows a two functioned receiver-transmitter. The receiver-transmitter responds differently to two different input signals. A first response is a pulse. A second response is a continuous signal.